The present invention is concerned with a slip-controlled hydraulic brake system for controlling fluid pressure in a wheel cylinder of a driven wheel of an automotive vehicle, during normal braking, brake slip control and traction slip control.
A brake system of this type is described by German Patent DE-38 32 023 A1. During brake slip control, this system operates on the back-flow principle, which involves pressure fluid flow from the outlet of a pump to a brake conduit in fluid communication with an inlet valve of a wheel brake and from an outlet valve of the wheel brake to the inlet of the pump. The pump of this system is a self-priming pump, which is also used for traction slip control. The pump takes in pressure fluid, through the master cylinder, from the pressure fluid reservoir, and feeds the pressure fluid into the wheel cylinder. The direct feed to the wheel cylinder results in the benefit that no additional high-pressure accumulator is required.
However, in systems of that type, especially at low temperatures due to the high viscosity of the pressure fluid, the response time of traction slip control is longer than the response time for systems having a high-pressure accumulator. A reason for the increased response time is because long-length conduits and a plurality of valves are provided between the pump and the pressure fluid reservoir, thereby constricting the volume flow and resulting in take-in losses.